Medical navigation allows medical instruments to be located and positionally traced (tracking) with the aid of a tracking and navigation system. The instruments shown can then be displayed on an image output (for example, a screen) in their correct or current positional relationship to a patient's body or parts of a patient's body, if the patient has been scanned by means of an imaging method (CT, MR, etc.) and registered in the navigation system beforehand. Within this setting, the present invention is intended to provide visual assistance in aligning and/or orienting instruments.
It is often necessary to exactly align instruments or to exactly plan their alignment, for example when implants have to be exactly placed at particular bone structure positions. The position of an implant is then for example set by a surgeon by considering adjacent anatomical landmarks, unique bone structures or pre-planned points and axes. When fixing a pelvic fracture, for example, the trajectory of the inserted screw has to have a specific angle to the lateral proximal femoral bone surface, i.e. usually about 130°. In order to set a suitable placement of the pelvic screw, a special drill guide is usually used which is pressed on the lateral cortex of the greater trochanter region. The guide hole of the drill guide is aligned such that its axis points to the femoral neck at an angle of 130° to the proximal femoral bone axis.
In this example, but also in other surgeries, a separate and dedicated tool is therefore required in order to be able to correctly insert a medical instrument. This special tool often also requires contact with bone structures or other body structures which are not normally exposed, such that an extensive and invasive preparation—i.e. opening up the patient—is often necessary.
The same problem also for example occurs when the entry point for specific implants has to be prepared, such as for example a lateral femoral nail, wherein a specific point on the lateral proximal femur has to be found by attaching a template. In this case, too, highly invasive preparations in the bone region are necessary.